1. Field of the Invention
This invention relates to electronic circuits, and more particularly, to efficient power management of peripheral port connections.
2. Description of the Relevant Art
A Universal Serial Bus (USB) is a standard serial bus interface for connecting devices, such as multiple computer peripherals or portable music and video players, to a host computer for easy transfer of data by means of hot swapping, or allowing devices to be connected and disconnected without a need to reboot the computer or to turn off the device. This means of connecting is also referred to as hot plugging. USB allows several devices to be used without requiring manufacturer-specific device drivers to be installed on the host computer. USB may also be utilized as a bridging power cord between a peripheral device and an AC adapter plugged into a wall plug for battery charging purposes. The USB Implementers Forum (USB-IF), an industry trade association incorporating companies from the computer and electronics industries, standardizes the design of USB. USB is intended to replace many legacy varieties of serial and parallel ports, and for many computer peripherals, USB has become the standard connection protocol.
USB interface is a master/slave architecture. The master is referred to as the “upstream” device or host/hub and the slave as the “downstream” device. The interface consists of four wires: D+, D−, VBUS, and Ground. The two data lines, D+ and D−, are for bi-directional data transfer and use differential drive techniques. The wires VBUS and Ground are used to distribute power from the upstream host to the downstream device.
USB devices are linked in series through hubs. A USB hub is a device that allows many USB devices to be connected to a single USB port on the host computer or another hub. USB hubs may be built into equipment, such as keyboards or monitors. Each hub has one upstream port and a number of downstream ports. The upstream port connects the hub (directly or through other hubs) to the host. Other hubs or devices may be attached to the downstream ports.
There are two types of hubs. First, a bus-powered hub is a hub that draws all its power from the host computer's USB interface. It does not need a separate power connection. A bus-powered hub is able to provide power to low-consumption devices without the need for an external power supply. However, many devices, or peripherals, require more power than this type of hub can provide, and therefore, these devices will not work with this type of hub. A second type, a self-powered hub, is a hub that draws its power from an external power supply unit. Therefore, a self-powered hub is able to provide full power to every port.
A USB is host controlled. There can only be one host per bus. The USB 2.0 Specification does not support any form of multi-master arrangement. The USB host is responsible for undertaking all transactions and scheduling bandwidth. Data may be sent by various transaction methods using a token-based protocol. Typically, a USB host controller is built into modern computers, while older computers can be updated with the hardware. For example, a hi-speed USB host controller may reside on a card that installs into any available slot on the motherboard. The back-facing plate of the controller provides two or more USB ports.
Both the USB host ports and the downstream USB hub ports require port power management. Port power management is defined in the USB 2.0 Specification, which is supported by the USB-IF, to include a power switch and over-current protection with reporting. An external Port Power Controller, available from multiple manufacturers, provides single or dual USB port support when used with a USB hub. However, backwards compatibility with legacy battery charging devices is problematic in that there is no standard method. Various manufacturers have devised several different methods. In addition, some methods interfere with normal USB operation. Further, more advanced power management functions are forthcoming in the USB Battery Charging Specification revision 2.0. A new capability is required for more advanced general port power management in the computing system.
In view of the above, efficient methods and systems for efficient power management of peripheral port connections is desired.